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Message-ID: <CALCETrXXzt8WZMs3dsReCJ5wdF3zhxFmUtGnmdCgV7_exFUKKQ@mail.gmail.com>
Date: Fri, 19 Jun 2020 11:00:28 -0700
From: Andy Lutomirski <luto@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: X86 ML <x86@...nel.org>, jpa@...nelbug.mail.kapsi.fi,
Dave Hansen <dave.hansen@...el.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] selftests/fpu: Add an FPU selftest
On Fri, Jun 19, 2020 at 10:41 AM Borislav Petkov <bp@...en8.de> wrote:
>
> From: Petteri Aimonen <jpa@....mail.kapsi.fi>
>
> Add a selftest for the usage of FPU code in kernel mode.
>
> Currently only implemented for x86. In the future, kernel FPU testing
> could be unified between the different architectures supporting it.
Acked-by: Andy Lutomirski <luto@...nel.org>
except:
> +#
> +# CFLAGS for compiling floating point code inside the kernel. x86/Makefile turns
> +# off the generation of FPU/SSE* instructions for kernel proper but FPU_FLAGS
> +# get appended last to CFLAGS and thus override those previous compiler options.
> +#
> +FPU_CFLAGS += -mhard-float -msse
> +ifdef CONFIG_CC_IS_GCC
> + ifeq ($(call cc-ifversion, -lt, 0701, y), y)
> + # Stack alignment mismatch, proceed with caution.
> + # GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3
> + # (8B stack alignment).
> + FPU_CFLAGS += -mpreferred-stack-boundary=4
> + else
> + FPU_CFLAGS += -msse2
> + endif
> +endif
This should be cc-option, not cc-ifversion, I think. But maybe we
should consider dropping the problematic GCC version instead? The old
GCC versions with stack alignment problems are seriously problematic
for x86 kernels, and I don't really trust kernels built with them.
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